1. Field of the Invention
This invention relates to novel polyindanebisphenols which are useful in the preparation of thermosetting polymers and thermoplastics. The polyindanebisphenols (xe2x80x9cPIBPxe2x80x9d) are prepared under acidic conditions from p-2-isopropenylphenol (xe2x80x9cIPPxe2x80x9d) and 1,3-, 1,4-, or 1,2-diisopropenylbenzene (xe2x80x9cDIPBxe2x80x9d) in quantitative yield. Molecular weight is controlled by the ratio of p-2-isopropenylphenol to diisopropenylbenzene. When copolymerized with other commercial resins such as cresol novolac epoxies, PIBP based polymers are characterized by high glass transition temperature (xe2x80x9cTgxe2x80x9d), low dielectric constant, low moisture absorption, low coefficient of expansion, low cost, and can be processed on equipment typically used for the production of epoxy based laminates.
2. Description of the Prior Art
Phenolic-based polymer resins such as cresol-novolacs are commonly used in the production of thermosetting polymers for electronics (printed wiring boards, encapsulents, molding compounds, electrical insulation), reinforced plastics, including fiber reinforced plastics (xe2x80x9cFRPxe2x80x9d), aerospace, coatings (industrial, can), and adhesives. Previously available polymers based, e.g., on cresol novolac epoxies, suffer from a number of drawbacks. These include: (1) 1-2% moisture absorption; (2) low Tg; (3) undesirably high dielectric constant and (4) brittleness.
The importance of these properties can be appreciated by considering, for example, that for polymers, as the temperature of the polymer increases, one or more temperature points are passed at which there is a modulus loss due to a glass transition. Each such temperature point is thus described as a glass transition point or Tg. Therefore, a high Tg is a desirable feature permitting a printed wiring board or similar such construct to operate at higher temperatures, e.g., in an environment that includes active electrical and/or electronic components, while maintaining its structural integrity.
These problems can be overcome by using a phenolic based resin which has inherently low moisture absorption, high Tg, and low dielectric constant. Polyindanebisphenol (xe2x80x9cPIBPxe2x80x9d) is particularly well suited to overcome these drawbacks because of the inherent stiffness of the indane polymer backbone and the hydrophobic nature of the polymer. However, due to the limitations of the previously available synthetic schemes, which resulted in prohibitive costs, PIBPs have not gained ready commercial acceptance for such purposes.
The synthetic chemistry of the polyindanes can be best appreciated by first considering the synthesis of a xe2x80x9cpolyindanebisphenolxe2x80x9d having a single repeat unit. For example, 1,1,3-trimethyl-3-(p-hydroxyphenyl)-5-indanol (xe2x80x9cTMHPIxe2x80x9d), as shown below: 
is well known and has been utilized to prepare numerous thermosetting and thermoplastic polymers (U.S. Pat. Nos. 4,175,175, 5,145,926 and 4,988,785; Wilson, J. C., 1975 Journal of Polymer Science, Polymer Chemistry Edition, vol. 13, 749; Y. Imai and S. Tassavori, 1984, J. Polym. Sci., Polym. Chem. Ed., 22, 1319. However, none of these have attained a commercial status.
TMHPI is prepared from the precursor IPP, which is obtained first by cracking bisphenol A, having the following formula: 
The cracking of bisphenol A is optionally conducted under acidic or basic conditions (e.g., in the presence of NaOH at 220xc2x0 C.), yielding IPP, plus phenol; having the following formulas: 
The fact that the cracking process yields a mixture containing phenol, as a contaminant, has heretofore been considered a serious shortcoming of this process. IPP is not only heat sensitive, but it will readily polymerize under cationic, anionic, and free radical conditions. Consequently, while it has heretofore been taught that isolation of phenol from IPP is required to produce TMHPI, the isolation of IPP from phenol is in fact difficult to achieve in sufficient yield. After isolation of IPP, dimerization can then be conducted under acid conditions at mild temperatures to produce TMHPI. Thus, there is a longstanding need in the art for a method of avoiding the isolation of IPP from phenol in the preparation of indanes that are derived from IPP.
In addition, polymers based on TMHPI do not provide significant improvements to the parameters of moisture absorption, Tg, dielectric constant and brittleness. For example, when comparing similar polymers based on Bisphenol A or TMHPI, there is only a modest increase (10-30xc2x0 C.) in glass transition temperature or Tg. For example, when TMHPI was polymerized with an equimolar amount of 4,4xe2x80x2-dichlorodiphenylsulfone to yield a polyethersulfone, a Tg of 215xc2x0 C. was reported, which is only 30xc2x0 C. higher than the commercial polyethersulfone-based on Bisphenol A (Tg=185xc2x0 C.). In another example, of TMHPI shortcomings, when TMHPI is polymerized with the diglycidyl ether of tetrabromobisphenol A, a composition used for the preparation of flame retardant printed wiring board laminates, a glass transition of only 142xc2x0 C. was obtained (U.S. Pat. No. 4,672,102). For this reason, polymers based on the TMHPI-type of indane structure have not achieved commercial success. Attempts to overcome these shortcomings have also led to investigation of polyindane compounds. The preparation of polyindane from the various DIPB compounds has been known since the late 1950""s (Y. V. Mitin, N. A. Glukhov, Dokl., 1957, akad. Nauk, SSSR 115, 97; H. Brunner, A. L. Pallwel, D. J. Walbridge, 1958, J. Polym. Sci. 28, 629).
One class of polyindanes are the xe2x80x9cunfunctionalizedxe2x80x9d polyindanes, i.e., polyindanes lacking additional functional moieties capable of crosslinking or curing in the presence of other potential copolymer/co-monomer resins, e.g., epoxies. Such unfunctionalized polyindanes can be prepared from a number of precursors, under cationic conditions, using either Lewis or Bronsted acids (O. Nuyken, G. Maier, D. Yang, M. Leitner, 1992, Makromol. Chem., Macromol. Symp. 60, 57-63; O. Nuyken, M. B. Leitner, and G. Maier, 1992, Makromol. Chem. 193, 487-500; F. Gruber, O. Nuyken, 1989, Makromol. Chem. 190, 1771-1790; F. Gruber, O. Nuyken, 1989, Makromol. Chem. 190, 1755-1770 and O. Nuyken, M. B. Leitner, G., Maier, 1991, Makromol. Chem. 192, 3071). Thus, any functionality which can be conveniently converted to the isopropenyl functionality is a suitable precursor to an unfunctionalized polyindane. For example, either of the following structures can be chemically converted into unfunctionalized polyindane: 
wherein X1 and X2 can be the same or different and can independently be any of Cl, OH, OCH3 and/or OCOCH3. Formula A is 1,4 diisopropenylbenzene and Formula B can be, e.g., xcex1,xcex1xe2x80x2-dihydroxy-1,4, diisopropylbenzene, 1,4-bis(2-chloroisopropylbenzene), 1,4-bis(2-methoxy isopropylbenzene and 1,4-bis(2-acetoisopropyl benzene). The resulting polyindane has the formula: 
wherein xe2x80x9cnxe2x80x9d is an integer representing the number of repeats of the bracketed moiety or unit. However, this class of polyindane compounds has also, heretofore, failed to provide any practical and economical solutions for any of the above-mentioned problems in the art. Nevertheless, the compounds of Formulas A and B are readily employed as precursers to the compounds of the present invention, as described hereinbelow.
In particular, unfunctionalized polyindanes are claimed to have a Tg range from 220-320xc2x0 C. and a decomposition temperature of 450xc2x0 C. In fact, the art has described a broad range of molecular weights and glass transition temperatures, which attest to the difficulty in preparing pure polyindanes without some level of undesirable unsaturation. However, no commercial products have resulted from these efforts, due to the many shortcomings of this class of compounds. For example, the heretofor reported process is known to provide only low molecular weight polyindanes of this class, i.e., molecular weights of substantially less than 5,000 Dalton (see, e.g., O. Nuyken, et al., 1992, Makromol. Chem. 193, 487-500). Despite the suggestion that higher molecular weights might be obtained (e.g., Fritz et al., 1972, J. Polymer Science Part A-1, 10:2635-2378; D""Onofrio, 1964, J. of Applied Polymer Science 8:521-526; and Brunner et al., U.K. Patent No. 864,275, the previously provided polyindane polymers have been described as brittle, confirming undesirable mechanical properties.
In addition, these unfunctionalized polyindanes have other major drawbacks specifically related to printed wiring board applications. For instance, these compounds have no gel point, cannot be cured and do not crosslink. Thus, they exhibit unacceptably high coefficients of linear expansion and, without a curing step, cannot be used in traditional processes to produce laminate compositions. Further, polymers prepared from unfunctionalized polyindanes melt and flow at the temperatures used for soldering. In yet a further disadvantage, unfunctionalized polyindanes cannot be reacted chemically with other resins used to produce printed wiring boards.
xe2x80x9cFunctionalizedxe2x80x9d polyindanes were also tried in an attempt to produce less brittle polyindanes suited for the preparation of thermoplastics and thermosets. These were prepared by controlling the molecular weight and introducing functionality into the polymer, e.g., by introducing various substituent moieties to prepare polyindane derivatives. This strategy has been employed for the preparation of telechelics having terminal R groups, where R was CH3, NO2, NH2, CO2H, NCO, and COCl (O. Nuyken, D. Yang, F. Gruber, G. Maier, 1991, Makromol. Chem. 192:1969.
However, the available synthetic routes to obtain useful functionalized polyindanes have remained too expensive for commercial purposes. Thus, only the methyl terminated polyindanes have been directly prepared using a cationic chain growth process involving diisopropenylbenzene and 1-isopropenyl-4-methylbenzene (Nuyken et al., 1992, Makromol. Chem., Macromol. Symp. 60, 57-63, Id.). Further chemical modification was necessary to obtain other functionalized polyindanes.
Thus, there remains a strong need in the art for polyindane compounds having all of the above-described desirable properties, e.g., reduced levels of moisture absorption; increased thermal stability; reduced dielectric constant and decreased brittleness, for this class of compounds, while being simple and economical to manufacture. In particular, there remains a need for functionalized polyindanes having all of the desirable properties of this class of compounds, and having a molecular weight of less than 2,000 which are not brittle and which can be reacted with other material, e.g., monomer compounds, for the preparation of thermosets and/or thermoplastics.
Accordingly, the present invention surprisingly provides compounds, including polymers, copolymers and polymer compositions, as well as processes for preparing the same, that solve these and other longstanding problems in the art. Thus, the invention provides for an unexpectedly improved type of polyindane, in the form of a polyindanebisphenol (xe2x80x9cPIBPxe2x80x9d) compound of formula I: 
wherein xe2x80x9cnxe2x80x9d (also referred to herein as xe2x80x9c(n)xe2x80x9d for ease of identification) is an integer indicating the number of repeats for the bracketed moiety.
The invention also provides for polymers or copolymers prepared including the new polyindanebisphenols, as well as various types of compositions, e.g., laminates, prepared therefrom. Further, the invention provides for methods of preparing the inventive PIBP compound and polymer compositions including the same. PIBPs having an average number of repeating units of less than 2 will flow and process much like cresol novolacs but may not yield physical properties which are significantly better than polymers produced from Bisphenol A. For example, when PIBP is crosslinked with an epoxy resin to produce a laminate, the low molecular weight PIBP fails to provide significant improvement in moisture absorption and Tg properties over Bisphenol A based laminates. Thus, the invention provides for PIBPs having an average number of repeating units of two or more. As a consequence, the PIBPs of the invention readily provide the heretofore unobtainable linear hydroxy functionalized polyindanes, and provide simple and economical processes for preparing these desirable compounds, while avoiding the complexity of previously required substitutions on the indane structure. Therefore, the PIBP compounds according to the invention are readily prepared with molecular weights that will vary with the desired application and that will be primarily determined by the number of the repeat units.
As the number of repeating units (n) is increased to more than 10, on average, some of the resulting polymers will be brittle and, if processed from solution, will have high viscosities. Nevertheless, PIBPs having average repeating units (n), e.g., ranging from about 3 to about 1000, or greater, but preferably ranging from about 3 to about 25, and more preferably from about 3 to about 10, are readily prepared. Generally, as will be appreciated by the artisan, routine screening of a range of PIBP products, even those with (n) of greater than 10, will readily identify those polyindanes according to the invention with properties suitable for particular purposes.
Thus, the polyindanebisphenols of the invention will have (n) values consistent with molecular weights ranging from about 450 to about 200,000 Dalton, or greater. Preferably, the molecular weights of the polyindanebisphenols of the invention will range from about 450 to about 100,000 and more preferably from about 450 to about 2,000. In one preferred aspect, the molecular weight will range from about 600 to about 1700 Dalton.
Most preferably, the polyindanes of the invention have hydroxy equivalent weights that range from about 371 to about 924 grams. The hydroxy equivalent weight is the number of grams of polymer yielding 1 molar equivalent of hydroxy functionality, and is indicative of the hydroxyl concentration of the inventive polyindanebisphenols. In a most preferred aspect, the molecular weights of the polyindanebisphenols will range from about 370 to about 680 Dalton. In another aspect the invention also provides for novel polymer and/or thermosetting systems or compositions that are prepared by reacting one or more forms of the PIBP compounds of the invention and one or more additional suitable monomer compounds to form PIBP derivatives. The artisan will appreciate that, as described herein, and simply for ease of description, the term xe2x80x9cpolymerxe2x80x9d or xe2x80x9ccopolymerxe2x80x9d may also describe the comonomer compounds that are used to form the various polymers, copolymers and/or thermosetting systems or compositions according to the invention. Thus, additional polymer or copolymer compounds that are contemplated according to the invention include any materials suitable for the preparation of a useful derivative of the PIBP compounds of the invention and include, simply by way of example, art known polymer-forming monomers such as a polyetheretherketones, polyethersulfones, polycarbonates, polyesters, polyindanediallylethers, polyindanedicyanates, polyindanebisepoxies and/or any suitable variations, derivatives or combinations thereof.
In yet another aspect, the invention also provides for novel copolymers that include epoxy compounds such as, for example, cresol novolac epoxy resins, bisphenol F epoxy resins, brominated epoxy resins, polyglycidly amine epoxy resins, bisphenol A-based epoxy resins, fused ring aromatic epoxy resins, tetramethylbiphenyl-based epoxy resins, naphthalene or anthracene polynuclear epoxy resins, and mixtures thereof, as well as other types of epoxy resins, discussed in more detail hereinbelow.
Novel processes for preparing the PIBP compounds of the invention are also provided. Generally, the processes provide for the steps of
(a) cracking bisphenol A to produce a mixture comprising p-2-isopropenylphenol and phenol, and
(b) copolymerizing the mixture of step (a) with an isopropenylbenzene compound in suitable polymerization medium to yield PIBP.
For example, the above described copolymerization of step (b) is readily conducted under acidic conditions and in the presence of phenol. Further, in a preferred process, the copolymerization of step (b) can be conducted as a two-step process, so that the reaction is conducted in the presence of, e.g., an effective amount of trifluoroacetic acid followed by treatment with an effective amount of, e.g., sulfuric acid. Other options, in addition to acid treatment, include, simply by way of example, contacting the polymerization medium of step (b) with an effective amount of a strong acid cationic ion exchange resin, such as a sulfonic acid functionalized fluoropolymer, a sulfonic acid functionalized styrene-divinylbenzene (H) ion exchange resins, and/or mixtures thereof. In a further aspect of the invention, a heterogeneous acidic bentonite clay, a Ziegler type complex and/or mixtures thereof can also be employed in the copolymerization step. In a preferred aspect, the Ziegler type complex is LiBuxe2x80x94TiCl4xe2x80x94HCl, Al(Et)3Ti(OBu)4xe2x80x94HCl and/or mixtures thereof are employed.
In another aspect, the p-2-isopropenylphenol is optionally separated from the phenol prior to step (b), by any suitable method or process. Generally, the polymerization medium includes any suitable solvent or solvents effective to solubilize the reactants and to support the polymerization reaction. Simply by way of example and without limitation, such a suitable solvent or solvent system includes nitrobenzene, benzene, toluene, hexane, 1,2-dichloroethane, tetrachloroethane, tetrachloromethane, and/or mixtures thereof. It will be appreciated that any art known polymerization accelerators, initiators and the like may be conveniently employed in conducting the polymerization process of the invention. Simply by way of example and without limitation, 2-ethyl-4-methyl imidazole and/or 2-ethyl imidazole may be readily employed for these purposes.
In yet another aspect, the invention also provides for improved laminates that employ and include the novel polyindanebisphenol compounds of the invention, as well as providing for methods of making such improved laminates. Given the novel polyindanebisphenols of the invention, the artisan will appreciate that any art-known methods may be employed to make any desired compositions benefitting from this improved material. Simply by way of example, one preferred method for preparing an improved laminate composition includes the steps of:
(a) mixing, in a suitable solvent, a polyindanebisphenol according to the invention with one or more other monomers that are suitable for forming a copolymer composition with the polyindanebisphenol;
(b) impregnating a suitable fibrous support material with the mixture of step (a)
(c) desolvating said impregnated support material under conditions effective to form a dry improved laminate composition.